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Commit 30650239 authored by Alistair Popple's avatar Alistair Popple Committed by Benjamin Herrenschmidt
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powerpc: Add an in memory udbg console 



This patch adds a new udbg early debug console which utilises
statically defined input and output buffers stored within the kernel
BSS. It is primarily designed to assist with bring up of new hardware
which may not have a working console but which has a method of
reading/writing kernel memory.

This version incorporates comments made by Ben H (thanks!).

Changes from v1:
	- Add memory barriers.
	- Ensure updating of read/write positions is atomic.

Signed-off-by: default avatarAlistair Popple <alistair@popple.id.au>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 5737789c

arch/powerpc/Kconfig.debug

+23 −0
Original line number Diff line number Diff line
@@ -262,8 +262,31 @@ config PPC_EARLY_DEBUG_OPAL_HVSI 
	  Select this to enable early debugging for the PowerNV platform

	  using an "hvsi" console



config PPC_EARLY_DEBUG_MEMCONS

	bool "In memory console"

	help

	  Select this to enable early debugging using an in memory console.

	  This console provides input and output buffers stored within the

	  kernel BSS and should be safe to select on any system. A debugger

	  can then be used to read kernel output or send input to the console.

endchoice



config PPC_MEMCONS_OUTPUT_SIZE

	int "In memory console output buffer size"

	depends on PPC_EARLY_DEBUG_MEMCONS

	default 4096

	help

	  Selects the size of the output buffer (in bytes) of the in memory

	  console.



config PPC_MEMCONS_INPUT_SIZE

	int "In memory console input buffer size"

	depends on PPC_EARLY_DEBUG_MEMCONS

	default 128

	help

	  Selects the size of the input buffer (in bytes) of the in memory

	  console.



config PPC_EARLY_DEBUG_OPAL

	def_bool y

	depends on PPC_EARLY_DEBUG_OPAL_RAW || PPC_EARLY_DEBUG_OPAL_HVSI

arch/powerpc/include/asm/udbg.h

+1 −0
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ extern void __init udbg_init_40x_realmode(void); 
extern void __init udbg_init_cpm(void);

extern void __init udbg_init_usbgecko(void);

extern void __init udbg_init_wsp(void);

extern void __init udbg_init_memcons(void);

extern void __init udbg_init_ehv_bc(void);

extern void __init udbg_init_ps3gelic(void);

extern void __init udbg_init_debug_opal_raw(void);

arch/powerpc/kernel/udbg.c

+3 −0
Original line number Diff line number Diff line
@@ -64,6 +64,9 @@ void __init udbg_early_init(void) 
	udbg_init_usbgecko();

#elif defined(CONFIG_PPC_EARLY_DEBUG_WSP)

	udbg_init_wsp();

#elif defined(CONFIG_PPC_EARLY_DEBUG_MEMCONS)

	/* In memory console */

	udbg_init_memcons();

#elif defined(CONFIG_PPC_EARLY_DEBUG_EHV_BC)

	udbg_init_ehv_bc();

#elif defined(CONFIG_PPC_EARLY_DEBUG_PS3GELIC)

arch/powerpc/sysdev/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -64,6 +64,8 @@ endif 


obj-$(CONFIG_PPC_SCOM)		+= scom.o



obj-$(CONFIG_PPC_EARLY_DEBUG_MEMCONS)	+= udbg_memcons.o



subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror



obj-$(CONFIG_PPC_XICS)		+= xics/

arch/powerpc/sysdev/udbg_memcons.c

0 → 100644
+105 −0
Original line number Diff line number Diff line 
/*

 * A udbg backend which logs messages and reads input from in memory

 * buffers.

 *

 * The console output can be read from memcons_output which is a

 * circular buffer whose next write position is stored in memcons.output_pos.

 *

 * Input may be passed by writing into the memcons_input buffer when it is

 * empty. The input buffer is empty when both input_pos == input_start and

 * *input_start == '\0'.

 *

 * Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp

 * Copyright (C) 2013 Alistair Popple, IBM Corp

 *

 *      This program is free software; you can redistribute it and/or

 *      modify it under the terms of the GNU General Public License

 *      as published by the Free Software Foundation; either version

 *      2 of the License, or (at your option) any later version.

 */



#include <linux/init.h>

#include <linux/kernel.h>

#include <asm/barrier.h>

#include <asm/page.h>

#include <asm/processor.h>

#include <asm/udbg.h>



struct memcons {

	char *output_start;

	char *output_pos;

	char *output_end;

	char *input_start;

	char *input_pos;

	char *input_end;

};



static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];

static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];



struct memcons memcons = {

	.output_start = memcons_output,

	.output_pos = memcons_output,

	.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],

	.input_start = memcons_input,

	.input_pos = memcons_input,

	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],

};



void memcons_putc(char c)

{

	char *new_output_pos;



	*memcons.output_pos = c;

	wmb();

	new_output_pos = memcons.output_pos + 1;

	if (new_output_pos >= memcons.output_end)

		new_output_pos = memcons.output_start;



	memcons.output_pos = new_output_pos;

}



int memcons_getc_poll(void)

{

	char c;

	char *new_input_pos;



	if (*memcons.input_pos) {

		c = *memcons.input_pos;



		new_input_pos = memcons.input_pos + 1;

		if (new_input_pos >= memcons.input_end)

			new_input_pos = memcons.input_start;

		else if (*new_input_pos == '\0')

			new_input_pos = memcons.input_start;



		*memcons.input_pos = '\0';

		wmb();

		memcons.input_pos = new_input_pos;

		return c;

	}



	return -1;

}



int memcons_getc(void)

{

	int c;



	while (1) {

		c = memcons_getc_poll();

		if (c == -1)

			cpu_relax();

		else

			break;

	}



	return c;

}



void udbg_init_memcons(void)

{

	udbg_putc = memcons_putc;

	udbg_getc = memcons_getc;

	udbg_getc_poll = memcons_getc_poll;

}